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From 1fa16daaa76d1b132c8fee027c11bad5a5d25761 Mon Sep 17 00:00:00 2001
From: Roland McGrath <roland@redhat.com>
Date: Tue, 14 Sep 2010 12:22:58 -0700
Subject: [PATCH 3/4] x86-64, compat: Retruncate rax after ia32 syscall entry tracing
In commit d4d6715, we reopened an old hole for a 64-bit ptracer touching a
32-bit tracee in system call entry. A %rax value set via ptrace at the
entry tracing stop gets used whole as a 32-bit syscall number, while we
only check the low 32 bits for validity.
Fix it by truncating %rax back to 32 bits after syscall_trace_enter,
in addition to testing the full 64 bits as has already been added.
Reported-by: Ben Hawkes <hawkes@sota.gen.nz>
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
---
arch/x86/ia32/ia32entry.S | 8 +++++++-
1 files changed, 7 insertions(+), 1 deletions(-)
diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 7f9eb54..4edd8eb 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -50,7 +50,12 @@
/*
* Reload arg registers from stack in case ptrace changed them.
* We don't reload %eax because syscall_trace_enter() returned
- * the value it wants us to use in the table lookup.
+ * the %rax value we should see. Instead, we just truncate that
+ * value to 32 bits again as we did on entry from user mode.
+ * If it's a new value set by user_regset during entry tracing,
+ * this matches the normal truncation of the user-mode value.
+ * If it's -1 to make us punt the syscall, then (u32)-1 is still
+ * an appropriately invalid value.
*/
.macro LOAD_ARGS32 offset, _r9=0
.if \_r9
@@ -60,6 +65,7 @@
movl \offset+48(%rsp),%edx
movl \offset+56(%rsp),%esi
movl \offset+64(%rsp),%edi
+ movl %eax,%eax /* zero extension */
.endm
.macro CFI_STARTPROC32 simple
--
1.7.2.3
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